1. Field of the Invention
The present invention relates to a method for mounting a luminescent device of mounting a luminescent device on a mounted board by a flip chip method or a face up method.
2. Description of the Related Art
A light emitting diode chip (which is hereinafter abbreviated as an LED chip) using a gallium nitride compound semiconductor (Al1-X-YInXGaYN, 0≦X≦1, 0≦Y≦1, 0≦X+Y≦1) capable of emitting blue light with a high light emission intensity is being subjected to practical use. Upon accumulating a gallium nitride compound semiconductor, epitaxial growth on an insulating growth substrate, such as a sapphire substrate, is often employed. Therefore, it is difficult to form an electrode on the side of the sapphire substrate, and both the anode and cathode are formed often on the side of the semiconductor layer.
An LED chip having the aforementioned structure is mounted on a mounting substrate mainly in one of the following two methods.
One of the methods is a flip chip mounting method, in which an LED chip is mounted on a mounting substrate with the semiconductor layer side thereof having the cathode and anode directed to the mounting substrate. In the mounting method, such a method for mounting an LED chip on a mounting substrate is subjected to practical use that: a solder layer is formed the anode and cathode of the LED chip; a solder paste is coated on the mounting substrate by screen printing; the LED chip is disposed on the mounting substrate with the semiconductor layer side thereof directed to the mounting substrate; and then the assembly is subjected to reflow (see, for example, JP-2007-266396).
The other mounting method is a face up mounting method, in which an LED chip is mounted on a mounting substrate with the growth substrate side thereof directed to the mounting substrate. In the mounting method, such a method for mounting an LED chip on a mounting substrate is subjected to practical use that: a metal having good wettability with solder, such as gold, is formed on the back surface of the growth substrate; a solder paste is coated on the mounting substrate by screen printing; the LED chip is disposed on the mounting substrate with the growth substrate side thereof directed to the mounting substrate; and then the assembly is subjected to reflow (see, for example, JP-2005-072148).
In the flip chip method and the face up method that use a solder paste, a flux, which is an organic activator for bonding, contained in the solder paste remains between the LED chip and the mounting substrate. The flux deteriorates the reliability of bonding between the LED chip and the mounting substrate, and therefore, the flux is necessarily removed by rinsing, which complicates the mounting process.
Furthermore, a solder paste that has been subjected to practical use contains only large microscopic solder particles having an average particle diameter of from 2 to 50 μm. Accordingly, the solder paste fails to pass favorably through a metallic mask upon screen printing, and precise transfer of the solder paste may not be expected. Consequently, the yield may be deteriorated in the flip chip method, in which failures due to short circuit between the anode and cathode are necessarily prevented.